Ship hull construction



July 15, 1969 E. A. NC'JNNECKE 3,455,263

SHIP HULL CONSTRUCTION Original Filed Oct. 15, 1965 4 Sheets-Sheet 1 AIL V INVENTOR- ERN 57' H. NZJ'NNEC/(E 1 Wm M W July 15, 1969 E. A. NONNECKE 3,

SHIP HULL CONSTRUCTION Original Filed 001;.15, 1965 v 4 Sheets-Sheet 5 INVENTOR m .043 H v v 4 m a m 1 l w M Q ERN5T A. NCNNECKE 7 MM wwd/ W E. A! NCNNECKE 3,455,263 's'nir HULL CONSTRUCTION Original Filed Oct. 15, 1965 I July 15, 1969 4 Sheets-Sheet 4 United States Patent 3,455,263 SHIP HULL CONSTRUCTION Ernst A. Niinnecke, Reesestrasse 9, Hamburg 22, Germany Continuation of application Ser. No. 496,424, Oct. 15, 1965. This application Jan. 30, 1968, Ser. No. 702,762

Int. Cl. B63b 1/08 U.S. Cl. 11457 17 Claims ABSTRACT OF THE DISCLOSURE This is a continuation of Ser. No. 496,424 filed Oct. 15, 1965, now abandoned.

This invention relates in general to ship hull construction and in particular to a new and useful hull construction for a ship having a single screw-propeller or a ship having a centrally located screw-propeller in which the hull in the vicinity of the screw on the side where the propeller blades move downwardly is formed differently and non-symmetrically in relation to the opposite side at which the propeller blades move upwardly in order to improve the conditions of flow toward the screw.

In the usual construction of hulls for single screw ships or ships having a central screw, the stern is designed symmetrically in relation to the vertical longitudinal median plane. However, with such a construction it has beenfound that the flow toward the propeller is appreciably more unfavorable on the side of the ship on which the propeller blades move upwardly than on the opposite side at which they move downwardly. The result of this is not only that the propulsion efliciency of the propeller is appreciably worse than the propulsion efficiency of a propeller in an indisturbed flow, but also that the hull design does not make it possible to increase the stern fullness (block coeflicient). By fullness herein is meant the ratio of the actual volume of the part of the ship under water to the volume of a block having a length corresponding to the length of a ship between plumbs, a width corresponding to the maximum width of the ship at the water line level, and a height corresponding to the depth of the immersed part of the hull. In conventionally designed hulls the possibility of increasing the fullness is limited because the water line inflow angles become excessive when optimum fullness is achieved, and passive, or even opposite, flows will occur. In addition, because of the non-symmetrical flow of water to the propeller, there periodically occur at the propeller hydrodynamic forces which are transmitted by the propeller into the line shafting and may produce rotary vibrations and bending vibrations in the line shafting and the machine which are transmitted through the bearings to the hull. It is known that with an even number of blades on the propeller the periodic variations of the propeller thrust and of the torque predominate while with an odd number of blades of the propeller the periodic variations of the transverse force and of the bending moments predominate. As the number of blades of the propeller are increased, the vibration exciting forces become smaller. Moreover, with the usual symmetrical design of the stern portion of the hull cavitations frequently occur at the ends of the propeller blades as the "ice blades come out of the wake area of the part of the stern frame lying above the stern tube.

It is already known to provide a hull design at the location below the stern which includes a guide fin for the water which is curved counter to the direction of rotation of the propeller so that a spin opposed to the direction of rotation of the screw is imparted to the water flowing toward the screw. By such a measure an improved fiow toward the propeller blades and hence an improved efficiency of the screw is achieved. However, such a provision does not provide any advantage in respect to the fullness of the stern.

In accordance with the invention there is provided a hull which is designed non-symmetrically so that the part of the stern lying above the propeller shaft on the side at which the blades move downwardly is notched or indented. Thus, in the zone of the propeller aperture, the center lines of the horizontal sections through the hull are inclined away from the longitudinal median plane of the ship in a direction opposite to the direction of rotation of the propeller, and this inclination is increased from the zone opposite the root of the propeller blades to that opposite to the ends of the propeller blades. As seen from the stern, the stern frame above the stern tube forms with the longitudinal median plane an angle inclined against the direction of rotation of the propeller. The part of the stern frame below the stern tube is designed in a known manner without a rudder pintle and is either cut away or constructed so that it constitutes in the lateral view of the ship approximately the vertical prolongation of the upper part of the stern frame.

With the inventive construction it is possible to provide a hull where the conditions of flow toward the screw are so improved that without loss of screw efiiciency, and, without increase of periodic hydrodynamic forces, the stern fullness can be increased.

Accordingly, it is an object of the present invention to provide a hull construction in which the stern fullness and the conditions of flow to the screw are vastly improved.

A further object of the invention is to provide a hull construction in which the stern is formed asymmetrically and the portion of the stern above the stern tube and adjacent the propeller aperture is provided with an indentation on the side of the hull at which the propeller blades move downwardly.

A further object of the invention is to provide a hull construction which is simple in design, rugged in construction and economical to manufacture and provides for increased efficieney of the operation of the screw and permits an efficient hull fullness.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

In the drawings:

FIG. 1 is a partial elevational view indicating the construction of the stern portion of the hull in accordance with the invention;

FIG. 2 is a rear view of the hull construction of FIG. 1;

FIG. 3 is a view similar to FIG. 1 of a slightly modified embodiment; and

FIG. 4 is a rear view of the embodiment indicated in FIG. 3.

Referring to the drawings in particular, the invention embodied in FIGS. '1 and 2 comprises a hull design in which the hull stern body is formed asymmetrically with an indentation or cavity formed directly above the opening for the screw on the side on which the blades rotate downwardly. The hull stern body is the main hull body at the stern. The direction of rotation of the screw is indicated by the arrow in FIG. 2. In the embodiment of FIGS. 1 and 2 the stern frame is cut away below the stern tube and the rear end of the keel is drawn obliquely up to the stern tube.

In the embodiment'of FIGS. 3 and 4, the hull design is substantially similar to that indicated in FIGS. 1 and 2, with the basic difference that the portion of the stern frame below the stern tube forms a prolongation of the portion of the stern frame above the stern tube with the formation being more vertical than that of the formation of the FIGS. 1 and 2 embodiment.

With the hull construction of the invention the water enters the propeller plane with initial spin which is directed counter to the direction of rotation of the propeller. Owing to this, the flow toward the propeller is appreciably better on the side of the stern on which the screw blades move upward as compared with the flow to a propeller in which a symmetrical design of hull stern is provided. As a result of this, one can increase the stern fullness as compared with that of the symmetrical design of the stern. The fullness may be increased until a nonsymmetrical design limit is reached at which the flow still just barely applies on the side on which the propeller blades move upwardly. The fullness can be practically increased at the stern to such an extent that the reduction of the propeller efficiency caused by the greater fullness cancels out the eificiency improvement due to the nonsymmetrical construction of the stern. In this way a considerable dead weight capacity gain can be accomplished especially in large ships with the low Froude index (F=v/ /g.L, where v=velocity of the ship in meters per second, g=gravity acceleration in meters per second/ per second, and L=length between the plumbs in meters, that is the length measured between the rudder axis and the intersection of stem and load line) and, consequently, a great fullness.

It should be appreciated that in accordance with the invention the improvement of the hull design to effect improved water fiow toward the screw alone may be employed to increase the velocity of the ship or may be employed to save machine power. Of particular significance economically, however, is the possibility of increasing the dead weight capacity.

Resistance and propulsion experiments have been carried out with a model of the inventive construction, using a model of a 100,000 ton dead weight tanker of normal stern form and another model having a non-symmetrical stern form in accordance with the invention. For both propulsion experiments the same four-blade propeller from the stock of the Hamburgische Schiifsbau-Versuchsanstalt (Hamburg Shipbuilding Experimental Institute) was used. The model was a separating one, so that the same bow form could be used for both experiments. Both ships have the same displacement and the same displacement distribution. The fullness degree of this displacement was 6pp=0.8l8. With the first model a speed of 15.18 knots was reached at a given power of 18,130 SI-IP. This result was verified with reference to the statistical documents in the hands of the Hamburg Shipbuilding Experimental Institute and the sketch was rated as good.

With the same power the model using a non-symmetrical stern of the invention had a speed of 15.30 knots. Thus, with the design of the hull according to the invention the speed was improved by 0.12 knot representing a power saving of 2.8%, that is, in the present case a saving of about 500 SHP. To be able to evaluate correctly the extent of this improvement for ships of this size, a study was made to determine to what displacement increase a velocity decrease of 0.1 knot corresponds. It was found that instead of a velocity gain of 0.1 knot the dis placement can be increased by 1,000 tons, which may be regarded as a dead weight capacity gain.

A further advantage of the present inventive hull design makes it possible to insure that great force variations do not occur simultaneously on two blades of the propeller. The number of blades on the propeller and stern form can be so matched that the force variations of the individual blades occur successively and that the sum of these force variations, that is the force engaging the propeller periodically, will remain small. This is true of a propeller having an even number of blades as well as a propeller having an odd number of blades. If the number of blades and the non-symmetrical stern are matched in the most optimium manner as is readily possible by a calculation based on model experiments, there applies for the design of the hull according to the present invention the rule that the vibration exciting forces become smaller with an increasing number of blades. This is so regardless of whether an even or odd number of blades is used.

When changing over from a propeller with four blades to one with five blades therefor, not Only do the periodic variations of the propeller thrust and of the torque become smaller, but also even though it is now a propeller with an odd number of blades, the periodic vibrations of the transverse force and of the bending moment become smaller. Theoretical considerations have shown that the favorable effect of the inventive hull design in respect to the reduction of the vibration exciting forces is far greater than the unfavorable effect on the vibration exciting forces caused by an increase of the fullness degree of the hull from 0.81 to about 0.82, if, based on model experiments and a calculation for the selected number of blades, the stern is shaped to obtain optimum conditions. The reduction of the vibration exciting forces obtained with the non-symmetrical design of the stern form as provided by the invention may also be used for reducing the number of blades of the propeller. For example, if the vibrations need not be reduced, instead of using a propeller With four blades, One with three blades may be selected. This of course means that a savings in cost for the propeller is achieved and at the same time a slight gain in propeller efficiency is obtained.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A ship having a hull stern body with an asymmetrical configuration, said stern body including an indented formation above the stern tube only on the side of the hull at which the propeller blade moves down Wardly.

2. A hull construction according to claim 1, wherein the hull extends substantially vertically from the stern tube down to the keel.

3. A hull construction according to claim 1, wherein said hull is formed obliquely from the stern tube to the keel.

4. A hull for a ship having a single screw-propeller or for a ship having a central screw-propeller, comprising a hull stern body formation which is non-symmetrical in that the part of the stern lying above the stern tube extends inwardly counter to the direction of screw rotation in relation to the part lying below the stern tube on only one side of said stern body so that in the zone of the propeller aperture the center lines of the horizontal sections through the hull are inclined away from the longitudinal median plane of the ship in a direction counter to the direction of rotation of the propeller and this inclination increases from the zone of the root of the propeller blades to that opposite the ends of the blades, whereby seen from the stern the stern frame above the stern tube forms with the longitudinal median plane an angle inclined away from the direction of rotation of the propeller.

5. A hull according to claim 4, wherein the number of blades of the propeller and the inclination of the stern frame part above the stern tube with respect to the stern frame part below the stern tube are selected so that only one propeller blade is opposite one stern frame part.

6. A method of increasing the propulsion efiiciency of a ship having a hull which is moved through the water by at least one propeller comprising inclining the horizontal sections of the hull body, on the side thereof in which the propeller turns downwardly, in a direction inwardly away from the longitudinal median plane of the ship and opposite to the direction of rotation of the propeller, and increasing this inclination from the zone opposite the root of the propeller blades to that opposite the ends of the propeller blades so that the stern frame above the stern tube forms with the longitudinal median plane an angle inclined against the direction of rotation of the propeller.

7. A method according to claim 6, wherein the stern frame below the stern tube is formed without a rudder pintle and is either cut away so that it constitutes, in the lateral view of the ship, approximately the vertical prolongation of the upper part of the stern frame.

8. A method according to claim 6, wherein the number of blades of the propeller and the inclination of the stern frame part above the stern tube with respect to the stern frame part below the stern tube are selected so that only one propeller blade is opposite one stern frame part.

9. A ships hull body construction comprising an asymmetrical hull body, a propeller for propelling the hull body through the water, the line drawing of said hull body body having a stern tube for the propeller located between water line 1 and water line 1 /2 and between station 0 and station /2; and in respect to the side of said hull body in which said propeller turns downwardly: a first longitudinal vertical plane line beginning at station 3 extending upwardly from a base line in a gradual curve which is indented slightly toward the bow adjacent water line 1 /2 and which is slightly above the center of rotation of the propeller, a second longitudinal vertical plane extending from station 2 in a gradually outwardly extending curve below water line 1 and in an inwardly extending curve adjacent water line 1 /2, a third longitudinal vertical plane-line extending from station 1 /2 rearwardly in a relatively deeply bulging concave curve in the vicinity of water line 1 and forwardly in a relatively deeply convex curve forwardly between water line 1 /2 and water line 2, and a fourth longitudinal vertical planeline extending from station 1 upwardly and rearwardly to the stern tube.

10. A ship's hull body construction according to claim 9, wherein the fourth longitudinal vertical plane line extending from station 1 extends substantially along the base line to station /2 and then extends sharply vertically upwardly to the stern tube.

11. A ships hull body construction according to claim 9, wherein the longitudinal vertical plane line from station /2 extends inwardlyabove the stern tube.

12. A ship having a hull stern body with an asymmetrical configuration, said stern body including an indented formation above the stern tube only on the side of the hull in which the propeller blade moves downwardly and extending inwardly at least to the longitudinal center line.

13. A ship, according to claim 12, wherein said indented formation extends inwardly beyond the longitudinal center line.

14. A ship hull body construction comprising an asymmetrical hull body, a propeller for propelling the hull body through the water arranged substantially at the longitudinal center line, the line drawing of said hull body indicating a hull asymmetry extending from a location slightly rearward of frame 0 forwardly up to about frame 3.

15. A ship hull body, according to claim 14, wherein the asymmetry extends over a ship length of more than 30% of half the length of the ship.

16. A ship hull body, according to claim 14, wherein said ships hull has a propeller located between frame 0 and frame /2 and wherein the asymmetry extends approximately 5 propeller diameters forwardly and approximately one propeller diameter rearwardly from the location of said propeller.

17. A ships hull body construction, according to claim 9, wherein a station line (1,,) extends from the longitudinal center line to the side of the hull at which the propeller turns downwardly, and thereafter upwardly above waterline 1 to the level of the propeller 1, thereafter upwardly and inwardly of buttock I to between waterline 1 /2 and waterline 2, and then curves in a direction opposite to the rotational direction above waterline 2.

References Cited UNITED STATES PATENTS 1,439,153 12/1922 Davis 1l4-57 ANDREW H. FARRELL, Primary Examiner US. Cl. X.R. 34 

